1. Field of the Invention
The present invention relates in general to an anti-squeal disc brake, and more particularly to improvements associated with transmission of tangential forces from friction pads to a torque member.
2. Discussion of the Prior Art
As described in Instruction Manual for Toyota Soarer (published in January, 1986), pages 4-87 and 4-88, a disc brake generally includes a disc rotor rotating with a wheel of a vehicle, a pair of friction pads each having a friction member and a backing plate secured to a back surface of the friction member, an actuator device for forcing the pair of friction pads against opposite friction surfaces of the disc rotor, for frictional contacts of the friction members with the friction surfaces of the rotor, and a torque member which is secured to a fixed member of the vehicle and which supports the pair of friction pads movably toward and away from the friction surfaces of the disc rotor, so that the torque member receives, through the backing plates, tangential forces which act on the friction pads during brake application.
Such a disc brake may under some conditions generate creaking or squealing noises during brake applications. This squealing phenomenon is considered to be caused by certain unstable vibrations due to an interaction between the disc rotor and the friction pads.
As indicated in FIG. 11 by way of example, when a friction pad 212 (only this outer pad being shown in the figure) is forced by an actuator device (not shown) against a rotating disc rotor 210, a tangential force F acts on the friction pad 212 in a direction parallel to a friction surface 214 of the disc rotor 210, by reaction of a friction force applied by the friction pad 212 to the disc rotor 210. This tangential force F is transmitted to a torque member 220, through a backing plate 218 secured to the back surface of a friction member 216 of the pad 212. Since a working point A at which the torque member 220 receives the transmitted tangential force F is spaced apart from the friction surface 214 by at least a distance equal to a thickness of the friction member 216, there arises a moment M in a clockwise direction (in FIG. 11) about the working point A. Consequently, the friction pad 212 is slightly displaced as exaggeratedly indicated in two-dot chain line in FIG. 11, in a direction that causes the surface pressure of the disc rotor 210 to rise on the leading side. Stated differently, the friction pad 212 tends to be forced against the friction surface 214 with a larger force on the leading side than on the trailing side. It is surmised that this phenomenon may cause unstable vibrations of the friction pad 212, which in turn may cause vibrations of the disc rotor 210, giving rise to operating conditions of the disc brake in which creaking or squealing noises are easily produced.
While the tangential force F is received by a wall surface of a cutout or slot formed in the torque member 220 to accommodate the friction pad 212 in the example of FIG. 11, it is presumed that a similar phenomenon takes place in the case where the tangential force is received by a pin 222 secured to a torque member, at a point B on the leading side of the rotor 210, as indicated in FIG. 12.